Bending machine and method for bending thermoplastic pipe material

Abstract

A bending machine is described for bending thermoplastic and heated pipe material (4) having an inner cross-section in a bending section of the pipe material (4), wherein the bending machine has a bending mandrel (14) to be arranged in the inner cross-section, which supports the heated pipe material (4) during a bending forming process in the bending section, and a mandrel drive that moves the bending mandrel (14) axially along the pipe material (4), wherein the bending mandrel (14) remains in the bending section after the forming process while the pipe material (4) cools, and the mandrel drive moves the bending mandrel (14) axially in the bending section one or more times before withdrawing the bending mandrel (14) from the cooled pipe material (4) of the bending section.

Description

[0001] The invention relates to a method for bending thermoplastic and heated pipe material having an inner cross-section in a bent section of the pipe material to be provided with a bend, wherein the heated pipe material is supported in the inner cross-section in the bent section by means of a bending mandrel during a bending forming process and the bending mandrel remains in the bent section after the forming process while the pipe material cools down.

[0002] The invention further relates to a bending machine for bending thermoplastic and heated pipe material having an inner cross-section in a bent section of the pipe material to be provided with a bend, wherein the bending machine has a bending mandrel to be arranged in the inner cross-section, which supports the heated pipe material in the bent section during a bending forming process, and a mandrel drive which displaces the bending mandrel axially along the pipe material, wherein the bending mandrel remains in the bent section following the forming process while the pipe material cools down.

[0003] Pipe material made of thermoplastic or thermoplastic fiber composite plastic must be heated and thus softened before bending. Furthermore, the pipe material must be stabilized in its inner cross-section to prevent it from being crushed or constricted during bending. After bending, the material must cool down again until it is dimensionally stable. The generic document DE 10 2012 005 973 A1 discloses the aforementioned bending machine with a bending mandrel for stabilizing the inner cross-section. During the bending process, the bending mandrel is located in the bending section of the pipe being bent. Fig. Figures 7c to 7h of the publication show various options for the bending mandrel. For example, it can be designed as a scale mandrel.

[0004] From DE 26 01 818 A1 a bending device and a method for bending thermoplastic pipe sections are known, wherein after heating the pipe section to hot forming temperature a support core is introduced into the pipe section and then the pipe section is bent around a bending piece, wherein the pipe bend thus obtained is removed from the bending device after cooling and the support core is removed.

[0005] Based on this, the invention is based on the object of increasing product quality when bending plastic pipes.

[0006] The object is achieved by means of a method having the features of main claim 1 and by means of a bending machine having the features of dependent claim 6. Further design features of the method according to the invention and of the bending machine according to the invention are the subject of subclaims 2 to 5 and 7 to 12, respectively.

[0007] A method is provided for bending thermoplastic and heated pipe material having an internal cross-section. It is to be provided with a bend in a longitudinal section, which represents a bending section. This bend is created by a forming process. During this bending and forming process, the heated raw material is supported internally by a bending mandrel that can be moved by the mandrel drive. Since the pipe material does not have sufficient inherent stability during the bending process due to the plasticizing heat, the bending mandrel temporarily remains in the bending section for a period of time after the forming process while the pipe material cools down. Once it has stabilized sufficiently, the bending mandrel can be withdrawn from the bending section.

[0008] The bending mandrel is not in a fixed position, neither relative to the pipe material in the bending section nor relative to the rest of the bending machine, but is moved axially one or more times by the mandrel drive in the bending section. Surprisingly, it has been shown that such a mandrel movement leads to a significantly improved surface quality of the outer and inner walls of the pipe material in the bending section after the forming process is complete and the pipe material has cooled. The surface is smoother. According to a discovery first attributable to the inventors, this is caused by the fact that unevenness present on the outer wall of the bending mandrel is evened out by the mandrel movement and is not transferred to the pipe material in the bending section.

[0009] To achieve this effect, the mandrel movement relative to the bending section occurs at a time when the pipe material is heated and softened. This is the case while it is being bent, or when it has already been bent but has not yet cooled down to the point where it is sufficiently rigid and inherently stable.

[0010] This allows for two variants, which can of course also be combined. For example, it is possible to perform the mandrel movement relative to the pipe material in the bending section during the bending forming process. Likewise, it is possible to perform the mandrel movement after the bending forming process is complete and the bending mandrel remains in the bending section while the pipe material cools. In both variants, it is particularly preferred to perform the mandrel movement while the bending section is located in a forming tool of the bending machine and is bent and / or held statically there.

[0011] The mandrel movement is particularly preferably a back-and-forth movement, preferably repeated. This is especially true when performed while the tube material is being bent during the forming process. However, it is equally possible to perform a single mandrel movement or multiple mandrel movements in one direction, for example, to retract the bending mandrel slightly.

[0012] The displacement of the bending head relative to the bending section must be distinguished from the retraction of the bending mandrel from the cooled and then inherently stable pipe material. The mandrel movement in the bending section occurs at a time when the pipe material has not yet cooled sufficiently for stabilization. After the mandrel movement, the pipe material is statically stabilized in the bending section for a certain period of time until it has cooled to the point where it has sufficient inherent stability and the bending mandrel can be withdrawn from the pipe material.

[0013] During draw bending, the tube material is drawn into the bending tool. Traditionally, the mandrel drive is stationary, causing the mandrel head to move axially within the tube material, i.e., to shift relative to the tube material. This movement is then superimposed on the axial mandrel movement caused by the mandrel drive, if the mandrel movement is performed during the forming process.

[0014] The design value for the length of the displacement path depends on the external structure of the bending mandrel. Particularly if it is designed as a sectional or scale mandrel, it has constrictions on its outer circumference and intermediate, comparatively thicker sections with a larger outer circumference. The same applies to a turned spring mandrel. These constrictions are located at a certain axial distance from one another. In the case of a scale mandrel, for example, this is defined by the axial length of the individual scales. To achieve good surface quality in the finished product, the displacement path is preferably greater than half the axial distance. This ensures that a thicker section in the tube material is moved to a location where a constriction previously existed. This achieves good uniformity, and the quality of the outer and inner walls in the bending section of the bent product is improved or even optimal.

[0015] In order to ensure that the mandrel movement relative to the bending section results in the smoothest possible outer surface of the bent pipe material and at the same time the displacement path of the axial displacement is minimized, it is preferable in a differently oriented dimensioning to design the displacement path no greater than 10% of the developed length of the bending section and / or no greater than the maximum internal cross-section of the pipe material.

[0016] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

[0017] The invention is explained in more detail below using exemplary embodiments with reference to the accompanying drawings, which also disclose features essential to the invention. These exemplary embodiments are for illustrative purposes only and are not to be interpreted as restrictive. For example, a description of an embodiment with a large number of elements or components should not be interpreted to mean that all of these elements or components are necessary for implementation. Rather, other embodiments may also contain alternative elements and components, fewer elements or components, or additional elements or components. Elements or components of different exemplary embodiments may be combined with one another unless otherwise stated. Modifications and variations described for one of the exemplary embodiments may also be applicable to other exemplary embodiments.To avoid repetition, identical or corresponding elements in different figures are designated by the same reference numerals and are not explained more than once. The figures show: Fig. 1 a bending machine for plastic pipe material with a heating device and a bending mandrel, Fig. 2 a bending mandrel to support the pipe material, Fig. 3 the insertion of the pipe material to be formed into a bending head of the bending machine of the Fig. 1, Fig. 4 the process of bending the Fig. 3 inserted plastic pipe and Fig. 5 and Fig. 6 Block diagrams of two possible process embodiments when operating the bending machine.

[0018] Fig. 1 schematically shows a bending machine 2 for bending thermoplastic pipes 4. This tubular material 4 is held by a pipe wrench 6. At the end of the bending machine 2 is a bending tool designed as a bending unit 8, which bends the plastic pipe 4. In the bending machine 2 shown, it performs the draw bend, in which the pipe material 4 is drawn into the bending tool, but can equally well perform the roll bend, in which the pipe material 4 remains at rest. Upstream of the bending tool is a heating device 10, which heats the pipe material 4 so that it can be bent. The heating device 10 heats the pipe material 4 to the softening temperature required for the bending process. It is then fed to the bending unit 8 for bending.

[0019] The bending machine 2 guides the workpiece, a thermoplastic pipe material 4, onto a bending mandrel 14, which acts as an internal mandrel and is inserted into the interior of the plastic pipe. The bending mandrel 14 supports the thermoplastic material. Unlike metal pipe material, the thermoplastic material must be heated to become bendable. This causes it to lose some of its rigidity.

[0020] Heating by heating device 10 occurs in a section of the pipe material 4 where a subsequent bend will be performed. This section is referred to here as the bending section. It is a length of the pipe material 4 that is heated and then advanced to the bending unit 8, which performs the bending on the heated and thermoplastically softened plastic material. In the bending machine 2 of the Fig. 1, the transport is a forward movement along the longitudinal axis defined by the machine bed. With other types of bending machines, the transport may be different, but this is irrelevant here.

[0021] The operation of the bending machine 2 and in particular the displacement of the pipe wrench 6 via its drive (not further designated) and the control of the bending unit 8 is carried out by a control device 12 which, for example, has a processor and an interface for inputting a bending program according to which the bending machine 2 then operates.

[0022] Fig. Figure 2 shows a schematic sectional view of an embodiment of the bending mandrel 14. It comprises a mandrel shaft 16 and a mandrel head 18, which is movably deflectable in all directions relative to the longitudinal axis defined by the mandrel shaft 16 - this is because the mandrel head 18 lies in the section of the pipe material 4 that is formed by the bending unit 8. During the bending process, the mandrel head 18 is located in the bend of the pipe created in the bending section and stabilizes the pipe material 4 in the inner cross-section so that it is not crushed or constricted. Mandrel heads of this type are known, e.g., from DE 10 2012 005 973 A1. They can be used here. Furthermore, it is possible for embodiments to design the mandrel head 18 as an articulated mandrel head or in the form of an elastic spring element turned along the axis of the mandrel shaft. The thorn head 18 of the Fig. However, the bending mandrel 14 shown in Figure 2 is designed purely as an example as a scale mandrel. It consists of individual scales 20 and has a guide cable 22 that runs from the head piece 24 of the mandrel head 18 through the mandrel head 18 and the mandrel shaft 16 to its rear, i.e., foot-side, end, and on which the individual elements forming the scales 20 are threaded.

[0023] A mandrel drive 26 axially displaces the bending mandrel 14 along the bending machine 2. It is controlled by the control device 12 and is axially displaceable relative to the pipe wrench 6 and thus the plastic pipe 4.

[0024] For the transformation, as it Fig. 3 shows the pipe material 4 being inserted into the bending machine 2 and held at its rear end (facing away from the bending unit) by the pipe wrench 6 and at its front end by the bending unit 8. In this state, the heating device 10 heats the bent section of the pipe material 4. Once the pipe material 4 has been sufficiently heated to its plasticizing limit, it is fed to a forming tool of the bending unit 8, here in the form of a bending disk 30 and a clamping jaw 32, which is then closed. A pleat smoother 31 and a counterholder 33 are arranged upstream of the forming tool.

[0025] The bending unit 8 now performs a bend, with the clamping jaw 32 and the bending disk 30 pulling in the pipe material 4; this is the so-called tensile bending. The mandrel head 18 stabilizes the inner cross-section of the plastic pipe. The pipe wrench 6, and thus the pipe material 4, are adjusted accordingly to match the bending process, which is achieved by controlling the pipe wrench 6 accordingly. The bending movement is in Fig. 4 by an arrow 34, which shows the movement of the forming tool in the bending section, which in Fig. 4 is designated by the reference number 28.

[0026] A double arrow illustrates that during this bending forming process, the mandrel head 18 is moved axially back and forth in the pipe material 4 by the corresponding action of the mandrel drive 26. This movement 36 therefore occurs both relative to the pipe wrench 6 and thus the pipe material 4, as well as relative to the machine bed, in particular relative to the wrinkle smoother 31 and the counterholder 33. If the mandrel drive 26 moves the bending mandrel 14 synchronously with the pipe wrench 6 during the draw bending process, the movement 36 is superimposed on this tracking movement. If no tracking movement occurs, the mandrel drive 26 exclusively causes the movement 36. This also applies in the case of a differently designed bending process, for example, during roll bending, in which the pipe material 4 remains stationary during the forming process.

[0027] This movement 36, which is exemplified here as multiple back-and-forth movements, can also be performed (either continuously or only starting) after the forming process is complete and the tube material 4 is still being held in a stabilizing position while it cools. It can also be performed as a single or multiple movement in only one direction.

[0028] The Fig. 5 and Fig. 6 show two variants in the form of a block diagram. In a first variant according to Fig. 5, in a step S1, the pipe material 4 with the bending mandrel 14 is inserted into the bending unit 8. This corresponds approximately to the state of the Fig. 3. The pipe material 4 is already heated here. Subsequently, in a step S2, the pipe material 4 is bent to form it. Once this deformation is complete, the bending unit or another suitable stabilizing device stabilizes the pipe material in a step S3 so that it can cool down. Before the pipe material has cooled down sufficiently to be removed, the bending mandrel is moved relative to the pipe material in a step S4 to improve the outer wall quality of the subsequent product. The bending mandrel 14 remains in the bending section 28, but is displaced axially therein, for example in a single movement or in a back-and-forth movement. Following this mandrel movement of the bending mandrel 14 relative to the pipe material 4 held in the bending head 8, carried out by the mandrel drive 26, is preferably followed by a rest phase, which is followed as a further cooling phase in a step S5.Once the pipe material has cooled sufficiently, it is removed in a final step S6.

[0029] Fig. Fig. 6 shows a second variant in which the mandrel drive 26 moves the mandrel head 18 in step S2, ie during the bending forming process (step S4). In other words, the mandrel movement of the mandrel head 18 relative to the pipe material 4 and relative to the bending machine 2 occurs during the bending process. Otherwise, steps S1-S5 correspond to the embodiment of Fig. 6 those of the Fig. 5. Of course, these two embodiments can also be combined by the mandrel drive 26 driving the mandrel head 18 both during bending ( Fig. 6) and also axially when the bend 34 has already been completed.

[0030] It is also possible to allow the back-and-forth movement 36 to transition directly into the withdrawal of the bending mandrel 14. The only essential factor here is that the back-and-forth movement 36 begins at a time when the tube material 4 has not yet cooled to sufficient inherent stability and is still being stabilized.

[0031] The following example bending processes were carried out on a Hot Bend 35 bending machine from WAFIOS AG, Reutlingen, Germany, with a modified control system. In the first processing step, a plastic pipe made of PA 12 with an outer diameter of 16 mm and a wall thickness of 2 mm was processed. It was heated using a contact heater with a heating element at 170°C to such an extent that the internal temperature of the pipe was between 140°C and 150°C. The bending machine was set to a bending radius of 40 mm. After heating, the workpiece was bent to a bending angle of 90°. After this forming process was completed, the bending mandrel was retracted by 3 mm, which corresponds to half the axial distance between two constrictions of the scale mandrel used in the bending machine.The plastic pipe was then allowed to cool for 10 seconds before the mandrel was completely withdrawn from the bending section, resulting in a travel of approximately 80 mm. After the mandrel head was withdrawn from the plastic pipe, the bent plastic pipe was allowed to cool for a further 30 seconds for safety reasons until it finally reached its final shape. The pipe was released from the bending tool after 30 seconds. The pipe bend produced in this way had significantly improved outer and inner walls compared to pipe bends produced without withdrawing the bending mandrel and with otherwise identical parameters.

[0032] In a second processing step, a plastic pipe made of PA 612 with an outer diameter of 36 mm and a wall thickness of 2 mm was formed. The contact heating temperature here was 205°C, and an internal pipe temperature of 170°C was reached. In contrast to the first processing step, the mandrel drive was controlled in such a way that the bending mandrel performed several back and forth movements during the forming process, i.e. during the forming activity of the bending head. The bending mandrel was advanced by 8 mm relative to the pipe material over 0.5 s, followed by a 0.01 s pause, after which the bending head was retracted by 8 mm over 0.55 s. This was followed by another 0.01 s pause. This mandrel movement sequence was then repeated several times until it lasted a total of 10 s. This time period corresponded to the duration of the bending forming process.The tube material was then cooled again for 10 s and the mandrel was then retracted, which in this case meant a travel distance of about 100 mm.

[0033] Here, too, it turned out that the outer wall of the finished product was significantly smoother than without the mandrel movement of the bending mandrel.

[0034] Above, the use of the bending mandrel 14 was explained using a bending machine 2 that heats, advances, and bends the pipe material 4 serially, i.e., performs individual bends one after the other. However, the advantages of the axial relative displacement of the bending mandrel 14 also apply equally to bending machines that do not move the pipe material during bending and / or that heat it substantially over its entire length beforehand. Examples include machines that place the completely heated pipe material into a bending mold, or that hold and bend it with several robot arms, or that perform roll bending on the stationary pipe material.

Claims

[1] Method for bending thermoplastic and heated pipe material (4) having an inner cross-section in a bending section (28) of the pipe material (4) to be provided with a bend, wherein the heated pipe material (4) is supported in the inner cross-section by means of a bending mandrel (14) which is axially displaceable by a mandrel drive (26) during a bending forming process in the bending section and the bending mandrel (14) temporarily remains in the bending section (28) after the forming process while the pipe material (4) cools down, characterized by that the bending mandrel (14) is axially displaced one or more times relative to the pipe material (4) in the bending section (28) by the mandrel drive (26) before it is pulled out of the pipe material (4) of the bending section (28). [2] Method according to claim 1, characterized bythat the bending mandrel (14) is axially displaced by the mandrel drive (26) during the forming process in the bending section (28), preferably axially back and forth once or several times. [3] Method according to one of the above claims, characterized by that the bending mandrel (14) is moved by the mandrel drive (26) after completion of the forming process in the bending section (28) and remains there while the pipe material (4) cools down. [4] Method according to claim 3, characterized by that the bending mandrel (14) rests in the bending section (28) after being moved while the pipe material (4) cools down. [5] Method according to one of the above claims, characterized by that the displacement is carried out while the bending section (28) is located in a forming tool (8) and is bent and / or held statically there. [6] Bending machine for bending thermoplastic and heated pipe material (4) having an inner cross-section in a bending section (28) of the pipe material (4) to be provided with a bend, wherein the bending machine has a bending mandrel (14) to be arranged in the inner cross-section, which supports the heated pipe material (4) in the bending section (28) during a bending forming process, and a mandrel drive (26) which displaces the bending mandrel (14) axially along the pipe material (4), wherein the bending mandrel (14) remains in the bending section (28) following the forming process while the pipe material (4) cools down, characterized by that the mandrel drive (26) axially displaces the bending mandrel (14) relative to the pipe material (4) in the bending section (28) one or more times before pulling the bending mandrel (14) out of the pipe material (4) of the bending section (28). [7] Bending machine according to claim 6, characterized bythat the mandrel drive (26) moves the bending mandrel (14) axially back and forth relative to the bending section (28) one or more times. [8] Bending machine according to claim 6 or 7, characterized by that the mandrel drive (26) leaves the bending mandrel (14) in the bending section (28) after the axial displacement while the pipe material (4) cools down. [9] Bending machine according to one of claims 6 to 8, characterized by that the mandrel drive (26) effects the axial displacement over a displacement path which is not greater than 10% of the length of the bending section (28) and / or which is not greater than the maximum internal cross-section of the pipe material (4). [10] Bending machine according to one of claims 6 to 9, characterized bythat the bending mandrel (14) has a mandrel head (18) to be arranged in the bending section (28), which has an outer circumference with constrictions which are axially spaced from one another, and that the axial displacement takes place over a displacement path which is at least as large as half the axial distance, wherein in particular the mandrel head (18) is designed as a segmented or scale mandrel. [11] Bending machine according to one of claims 6 to 10, characterized by that the mandrel drive (26) displaces the bending mandrel (14) axially relative to the bending section (28) during the forming process. [12] Bending machine according to one of claims 6 to 11, characterized by that the mandrel drive (26) carries out the displacement while the bending section (28) is located in a forming tool (8) of the bending machine and is bent and / or held statically there.

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